1. Field of the Invention
The present invention relates to a permanent magnet rotating machine available for motors and generators, and more specifically to an axial gap type permanent magnet rotating machine in which rotors and a stator are arranged in the direction along a rotating shaft so that the rotors are oppositely disposed with the stator being interposed therebetween.
2. Description of the Related Art
There are various types of rotating machines used in a motor or a generator, including both a type that uses a permanent magnet as a magnetic field system and a type that uses a coil as a magnetic field system. While each type has its advantages and disadvantages, a permanent magnet rotating machine that uses a permanent magnet as a magnetic field system is generally employed when electric generation efficiency is important. This is because, when both types of the magnet rotating machines having the substantially same physical size are compared, the magnet rotating machine using a permanent magnet as a magnetic field system generates a magnetic field stronger than that of a generator using a coil as a magnetic field system. Thus, the density of magnetic flux that links with an armature coil increases, which results in a higher induced voltage.
From a viewpoint of structure, the permanent magnet rotating machines are classified into a radial gap type and an axial gap type. The radial gap type permanent magnet rotating machine comprises a cylindrical rotor, around which more than one magnet with a radial magnetization direction are disposed in the circumferential direction of the rotor, and a cylindrical stator that is located radially outside or inside the rotor and has coils arranged to face the permanent magnets. Since this rotor radiates magnetic flux only from its circumferential surface, the interior space of the rotor is an electrically useless space.
On the other hand, the axial gap type permanent magnet rotating machine comprises disk-shaped rotor that is fastened to a rotating shaft, and a stator that is disposed to face the rotor in the direction along the rotating shaft. The rotor has more than one permanent magnets fastened thereto, and the stator has more than one coils which are fastened thereto so as to respectively face the permanent magnets. Arranging two rotors on either side of a stator enhances the magnetic effect. Furthermore, owing to the recent improvement of the performance of permanent magnets, sufficient output has become ensured even if no iron core is provided in the coil. It is of course that further output can be provided when an iron core is provided in the coil.
Thus, with the axial gap type permanent magnet rotating machine, magnetic flux is radiated from a disk-shaped plane. Accordingly, if a structure in which such disks are stacked is employed, many surfaces from which magnetic flux radiates are formed in the interior space of the rotor. As a result, compared with the radial gap type permanent magnet rotating machine, the axial gap type permanent magnet rotating machine would be able to provide higher output per volume.
In the present state, however, the radial gap type is more commonly used. As one of the reasons therefor, it has been pointed out that, compared with the radial gap type, the axial gap type has a complex structure and is difficult to fabricate.
When a magnet is mounted on a rotor disk, as shown in FIG. 10, guide pins 113 are sticking up perpendicularly on a rotor disk 103, each magnet 104 is moved close to the rotor disk 103 from above through the guide pins 113, and the magnet is secured to the rotor disk by bonding, screwing, etc. For example, JP 2009-33946 A (in a schematic view), teaches mounting a magnet onto a rotary table from above of the rotary table. An attractive force of a small magnet is not so great. However, a larger rotating machine uses a larger magnet which provides a greater attractive force.
Furthermore, as shown in FIG. 11, it is required to form a gap for containing therein a stator coil by combining the rotors, each having the rotor disk 103, on which the magnets 104 are mounted, so as to face each other with a spacer 105 or the like being interposed therebetween. As a result, however, the magnetic attractive force between the rotors becomes strong, which makes it difficult to manufacture a large axial gap type rotating machine.